1. Field of the Invention
The present invention relates in general to document distribution systems for transmitting a data file from one computer to another and in particular to a method for licensing the use of a document distribution system.
2. Description of Related Art
One important benefit of computer networks is that they allow a data file to be quickly transported from one location to another where it may be processed by software in the receiving computer. Computer networks commonly transport many kinds of data files, including for example, files defining documents to be printed or displayed by the receiving computer and files containing audio and video recordings that may be processed by the receiving computer to produce audio sounds or video displays.
A data file distribution system requires software in one or more source computers to send out the data file and software in one or more destination computers to receive and possibly process the data file. Software developers want to be compensated for the file distribution and processing software they develop. In many systems files are created by a relatively few commercial sources that are willing and able to pay license fees for the software they use to create the data files. However the data files are distributed to a relatively large number of non-commercial users that are less willing and able to pay licensing fees for the software they use to process the data files. Thus there has been many cases where software developers license software that creates and/or distributes data files for a fee but license software that receives and/or processes the data files free of charge. By creating a wide base of users that can process a particular type of file, the software developer creates a market for their file creation software.
Computer programs represent documents that may be printed or displayed using a large variety of file formats and although we can easily transmit a document file from one computer to another via a network or other means, we can't always be sure that the receiving computer will be capable of handling the document's particular file format. The popular “Acrobat” system for distributing documents requires a program in a sending computer to first convert a document file into a standardized “pdf” format. All computers receiving pdf files must use “viewer” software capable of processing pdf format files and displaying or printing the documents they describe. One reason the Acrobat system is widely used is that the system distributor provides viewers capable of reading the pdf format free of license charge to anyone who wants one. The system distributor charges only for the software needed to convert source document files into the pdf format. The existence of a large base of viewers encourages people who want to distribute documents to purchase and use the pdf conversion software.
One major drawback to the Acrobat system is that since the process converts a source document file to another (pdf) format, the document that is printed or displayed by the receiving computer from the pdf format file does not always exactly match the document that might have been printed or displayed by the software that created the original source file. This can happen, for example, when the Acrobat formatter may not have been updated to accommodate changes in the source file format employed by the software that created the source file. Also when there is no direct pdf format equivalent to a document feature defined in a source file the Acrobat formatter must either omit the feature from the document described by the pdf file or must approximate the feature with the nearest pdf equivalent. Also an Acrobat system will be unable to process a source file in an unknown format.
When a source program such as a word processor or graphic program prints a document it typically invokes the computer operating system's graphical description interface (GDI) which works with a printer driver to convert the document file to a “print file” that is then sent to a printer. The print file is a sequence of commands telling the printer how to print the document. One way to ensure that a receiving computer prints a document that closely matches a document that the source program would have printed is to simply send the print file generated by the source program to the receiving computer. The receiving computer can then forward the print file to its own printer. Any variation in the appearance of the document would be due only to variations between printers and would not arise from any inaccuracies in file format translation. A print file can also be used to transmit a document to be displayed on a screen instead of printer since some prior art viewers are capable of displaying a document on a video screen based on information contained in a print file.
Thus a system using standard print files for controlling printers as a medium for forwarding documents is likely to provide more accurate document reproduction than a system that translate source files into a standard document file format that does not directly control a printer. A print file-based system is also easier to maintain because such a system does not have to know how to translate a large number of document formats into a standard format. The printed output is the best representation of the document. Almost all source programs that create document files are capable of using an operating system's GDI and printer driver to convert document files into standard print files.
One reason that print file-based document distribution is not as widely used as the Acrobat system is that a would-be developer of such a system has little incentive to distribute free viewers capable of displaying and printing documents from print files. Unlike the Acrobat system, there is no opportunity for licensing file translation software because no translation program is needed; the source programs that create documents are themselves capable of generating the necessary print files. Although it is possible to charge a license fee for print file viewer software, a document distribution system that charges a viewer license fee may be less likely to be widely accepted than a document distribution system that only charges a license fee for software that distributes documents.
What is needed is licensing system by which a software distributor can provide software for receiving and processing data files of a standard format free of charge while obtaining a licensing fee from those who distribute those data files, even though the data files may be created by software that the distributor has no power to license.